$-8lm - 2m - n + 7 = 10m + 3n - 2$ Solve for $l$.
Combine constant terms on the right. $-8lm - 2m - n + {7} = 10m + 3n - {2}$ $-8lm - 2m - n = 10m + 3n - {9}$ Combine $n$ terms on the right. $-8lm - 2m - {n} = 10m + {3n} - 9$ $-8lm - 2m = 10m + {4n} - 9$ Combine $m$ terms on the right. $-8lm - {2m} = {10m} + 4n - 9$ $-8lm = {12m} + 4n - 9$ Isolate $l$ $-{8}l{m} = 12m + 4n - 9$ $l = \dfrac{ 12m + 4n - 9 }{ -{8m} }$ Swap the signs so the denominator isn't negative. $l = \dfrac{ -{12}m - {4}n + {9} }{ {8m} }$